This invention relates to the field of shut-off valves for fuel dispensing systems. More specifically, this invention relates to shut-off valves of the type having a main poppet and a downstream secondary poppet, with a shear groove therebetween.
Fuel storage and dispensing systems for service stations and the like typically include an underground fuel storage tank from which fuel is pumped to one or more above-ground fuel dispensers. It has become standard practice to place a shut-off valve in the fuel delivery pipe feeding each dispenser, the valve being advantageously located a short distance beneath the surface on which the dispenser sits. The primary purpose of the shut off valve is to stop the flow of fuel to the dispenser in response to a collision or physical shock sufficient to damage the delivery pipe and/or other components of the delivery system, thereby substantially preventing or minimizing fuel spillage. Many shut off valves also include a heat-sensitive fusible link in the valve mechanism, whereby the valve is closed in response to a fire.
Examples of prior art shut off valves are disclosed in the following U.S. Pat. Nos. 2,048,388--Johnsen; 2,898,926 Tsiguloff; 2,910,080--Wright et al.; 2,962,035--Wright et al.; 2,965,116--Boone et al.; 3,209,773--Klaus; 3,378,021-- Milo; 3,489,160--Moore; 3,515,157--Milo; 3,647,182--Boudot et al.; 3,709,240--Milo; and 3,860,024--Turley.
One type of shut off valve that has come into increasing use is the so-called "double poppet" shut off valve. In the double poppet valve, a main poppet valve provides the primary shut off function in response to a physical shock and (if it includes a fusible link) to fire. A secondary poppet, located in the valve housing downstream from the main poppet seat, is held open by the pressure of fluid flowing through the valve housing from the inlet to the outlet. The secondary poppet thus functions as a check valve, closing when fluid ceases to flow upwardly from the tank to the dispenser. Typically, the valve housing has a weakened, frangible, annular wall section, or "shear groove" just upstream from the seat for the secondary poppet. The shear groove is designed to fracture in response to shear forces above a predetermined magnitude (such as from ground heave or from a collision between a vehicle and the dispenser), thereby providing shock isolation for the delivery system components located upstream from the shear groove. Any shock strong enough to fracture the shear groove will also close the main poppet. Fluid flow through the valve housing is thus blocked, causing the secondary poppet to close, and thereby containing any backflow from the dispenser to minimize spillage.
One drawback to the typical double poppet shut off valve is that the entire valve must be replaced, at substantial cost and inconvenience, whenever the shear groove fractures, since the shear groove is an integral part of the housing between the main and secondary poppets.
Accordingly, it would be desirable to have a shut off valve that has the advantages of the double poppet type of valve, but which does not require replacement of the entire valve structure in the event of a shear groove fracture.